The Ultimate Guide to Crop Factor

In the photography world, whether you just became a part of it or you have been shooting for a while, the term crop factor is something that comes up very often. Since there are so many cameras and camera systems available now, this term is very popular in product specifications, marketing materials, articles, books, and even in conversations between photographers.

So, if you are a beginner in photography and want to learn about crop factor, I will try to make it easier for you to understand it.

Before there was digital, 35mm film was a standard format because of its huge popularity. In cases of using a 50mm lens on an SLR film camera, it was exactly known what it looked like in terms of field of view and the resulting image. Therefore, it was easy to understand and discuss different lenses and focal lengths.

Because of technological challenges and high manufacturing costs, it was impractical to make a digital camera sensor sizes that match the 35mm size. Due to this, camera manufacturers started out with a smaller sensor in digital SLR cameras. It was very important to keep the camera mounts and lenses the same so that the transition from film to digital goes as smooth as possible.

But there was a problem with using a smaller sensor; field of view and captured images appeared narrower due to the corners of the image frame were getting cropped—chopped off.

Lenses project a circular image, but the sensor only records a rectangular portion of the scene. That means that the rest of the scene gets thrown away. Now, if the sensor covers the full area of the image circle that is called a full-frame sensor, but if it covers a smaller part that throws away a part of the image that is called a crop sensor.

What it’s important for you to know is that full-frame sensors have the same physical size as 35mm film, but the crop sensors are smaller and can vary in size, depending on the system and the manufacturer.

Sensor Sizes and Crop Factors

Even though crop sensor and full-frame are very common names for digital sensors, there are some manufacturers who name cameras and sensors differently. Nikon, for example, refers to its full-frame cameras as FX and crop sensors cameras as DX. Others refer to cameras by 35sensor sizes, like 35mm or APS-C.

But you have to remember that although the lens and its focal length might be the same if you capture one scene with a smaller sensor than full-frame / 35mm film will proceed a different, narrow field of view.

A great way for you to understand and remember this effect is to use a real photo. For example, if you take an 8×10 photo and cut the edges of the photo with scissors to make it a 6×8, you are basically doing the same thing as a crop sensor. But, there is a catch and that is a sensor resolution that makes the image appear more magnified.

What is Crop Factor?

Now that you understand how using cameras with different lenses affect the field of view and the resulting image, you should get familiar with the crop factor itself. So what is it and what does it do?

For the purpose of better understanding what the field of view of a lens will look like when compared to a 35mm film or full-frame camera, manufacturers came up with a way to calculate the equivalent focal length of a lens.

Because the corners of the image are cropped, a wide angle lens isn’t that wide anymore, but a telephoto lens can make things appear closer. So, the crop factor is actually the relation of the sensor size to 35mm / full frame.

If you take the provided crop factor number, multiply it by the focal length of the lens, you will get the equivalent focal length relative to 35mm film / full-frame.

Now, for example, Nikon’s ’’DX’’ camera’s crop factor is 1.5x, so when you take a 24mm wide angle lens and multiply it with this number, the result you get is 36mm. What it means is that the 24mm lens on the crop sensor DX camera would be more like a 36mm lens on a full-frame camera when it comes to the field of view.

Basically, if you initiate a24mm lens on this crop sensor camera and then initiate a 36mm lens on a full-frame camera, if you put them next to each other and take pictures of the same subject at the same distance, you will see that both give a very similar field of view. But, you should know that this doesn’t mean that the resulting images would be identical. If you change focal length or a camera subject distance, it would have a drastic effect on perspective, depth of field and background blur.

List of Cameras and Their Crop Factors

1.5x Crop Factor

Nikon DX (Coolpix A, D3300, D5500, D7100)

Pentax K-5 II

Sony A5100, A6000

Samsung NX1

Fuji X-A1, X-M1, X-E2, X-T1, X-Pro1

1.6x Crop Factor:

Canon Rebel 70D, 7D Mk II, EOS M2

2.0x Crop Factor / Micro Four Thirds:

Olympus OM-D Series

Panasonic DMC Series

2.7x Crop Factor:

Nikon CX (J4, S2, AW1, V3)

Sony RX100 III, RX 10

Samsung NX Mini

How Crop Factor is Calculated

The math is quite simple! When you know the physical size of the sensor, the first thing you do is calculate the diagonal using Pythagorean Theorem (a² + b² = c²) and then you divide the number by the diagonal of the crop sensor.

What we can see is that the crop factor of the Nikon CX sensor is 2.73x, but it is usually rounded to 2.7x.

Common Crop Factors and Equivalent Focal Lengths

Here is a list of the common focal lengths and crop factors with resulting equivalent focal lengths:

35mm 1.5x 1.6x 2.0x 2.7x

14mm 21mm 22.4mm 28mm 37.8mm

18mm 27mm 28.8mm 36mm 48.6mm

24mm 36mm 38.4mm 48mm 64.8mm

35mm 52.5mm 56mm 70mm 94.5mm

50mm 75mm 80mm 100mm 135mm

85mm 127.5mm 136mm 170mm 229.5mm

105mm 157.5mm 168mm 210mm 283.5mm

200mm 300mm 320mm 400mm 540mm

What you can see is that the size of the sensor and its crop factor can have a big effect on the equivalent focal length of a lens. For example, a 200mm lens on a small sensor with a 2.7x multiplication factor can produce an equivalent focal length of 540mm.

Equivalent Focal Length

Now, here is where things can get complicated and confusing for many photographers. So, the focal length of a lens is the physical property of a lens and it can never change regardless of the camera sensor.

What you should remember is that when you look at the list above, you should always keep in mind that the smaller sensor is not just magically transforming your lens into a longer lens, it’s just cropping a lot of the image.

Lens Size / System Size

Manufacturers quickly realized that there were benefits from using a smaller sensor. Since edges of the image circle were not being used, they realized they could make smaller lenses that used less glass, which allowed more compact and lightweight lens design.

So that’s how smaller and lighter lenses were made, and then as technology progressed, came new mirrorless cameras that were specifically made with the crop sensor and smaller lenses to be compact and light.

Nowadays when we evaluate DSLR lenses, you will very often come across lenses that are made just for crop sensor cameras. Because of their smaller image circle, it is possible that they don’t work at all on full-time cameras, or they do work but display very dark corners.

So, to make it easier for potential buyers to make difference between lenses specifically designed for crop sensors, manufacturers gave different symbols and added them to lens names.
This is the list of the symbols for crop sensor lenses:

Nikon: DX

Canon: EF-S, EF-M

Sony / Konica Minolta: DT, E

Pentax: DA

Samsung: NX

Sigma: DC

Tamron: Di II

Tokina: DX

For example, if you look at a Nikon lens and see DX on its label, it shows you that the lens is designed to be used only on crop sensor Nikon DX cameras, while Canon lenses will clearly specify EF-S for theirs.

Same Mount, Different Lenses

What you should remember is that some lenses are specifically made to be used on crop sensor cameras, while there are standard full-frame / older 35mm film cameras that will work on both crop sensor and full-frame cameras.

Also, it is very common to see the same mount size but lenses that are designed for different sizes at some manufacturers. Let’s take Nikon’s F mount for example. It will allow mounting both full-frame and DX lenses.

The same is with Sony’s mirrorless cameras with the same Sony E-mount but lenses that are designed specifically for crop sensor Sony cameras such as Sony A6000 and Sony A6300, or full-frame lenses that will work on both.

Let’s take Sony A7 II and Sony A6000 and compare them.

So, they both have the same E-mount, but there is a big difference in sensor size. So when purchasing lenses for the A7 II, you will have to buy full-frame FE lenses, but in the case of A6000, you are able to use both FE / full-frame lenses and regular E series lenses with smaller image circle.

What’s important is to understand that the best lenses for digital cameras are often full-frame lenses. That is why they are usually more expensive and can keep better value over time than their smaller counterparts.

Sadly, neither Nikon nor Canon are eager to produce higher quality lenses for their crop sensor cameras. They both have only a couple of professional-level lenses, but the rest of the line is mostly composed of slow zoom lenses.

Sensor Size vs. Resolution

Now, even though it’s true that cutting edges of the frame to get a 6×8 photo is similar to what a crop sensor does, there is one important factor that we shouldn’t forget about and that is sensor resolution.

As every digital camera sensor is composed of many pixels, it seems logical that using a smaller sensor would translate to fewer pixels. But, that is not the case. If the sensor is made with physically smaller pixels than two sensors could have the same resolution because in some cases a crop sensor could have more pixels than a full-frame sensor.

Let’s take Nikon D4, for example. It has 16 million pixels on its full-frame sensor measuring 36.0 x 23.9mm. Now, Nikon D7000 also has 16 million pixels on its 23.6 x 15.6mm sensor.

With such a big difference in sensor size but the same number of pixels, the difference between these two is the actually the physical size of each pixel.

Nikon D4s has a lot bigger pixels measuring 7.3 µm. Nikon D7000 pixels are much smaller at 4.78 µm. That shows us that those pixels are practically packed closer together.

Since smaller pixels translate to more noise and less dynamic range in images, Nikon D7000 can’t match the image quality of the Nikon D4 in low-light situations. Because of that, manufacturers are very eager to talk about megapixels and not about sensor sizes.

The plan is to make you pay attention to the fancy megapixel number because they don’t want to mention how small the sensor actually is.

The good thing is that modern crop sensors have gotten very good at handling noise, especially at low to medium ISO levels. With good light, you’ll have a hard time seeing differences in image quality between a full-frame and a 1.5-1.6x crop sensor.

So it’s not all bad. There are some advantages to crop sensor cameras here. In good light, smaller pixels do very well, so if two sensors of different sizes but the same resolution perform in the same way in daylight, the camera with a smaller sensor could be favorable for getting closer to the action.

Even though you crop the image you magnify it at the same time. Let’s take a familiar example of an 8×10 printed photo. Now imagine cutting the corners of the photo to get a 6×8. But when you get 6×8 you enlarge it to another 8×10 photo. That’s basically the case here.

I hope that this article was helpful to you to understand crop factor. The most important thing for you to remember is that you shouldn’t be afraid of all the technicalities. Just learn to use the gear you own and focus on taking better pictures. That is all that matters.

About the AuthorChelsea Lothrop is a New England-based photographer specializing in equine, pet, and portraiture photography. In addition to pet photography, she likes photographing families and children.

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6 responses to “The Ultimate Guide to Crop Factor”

However, occasionally, authors of your advice, while they may be excellent photographers, are poor writers, rendering opinions that are less valuable than they could be.

Your piece today (Sept. 1) on the crop factor is a case in point. There are several sentences and paragraphs that are incomprehensible. I’ll point to just one example:

“But you have to remember that although the lens and its focal length might be the same if you capture one scene with a smaller sensor than full-frame / 35mm film will proceed a different, narrow field of view.”

I urge you to cast a sharper editorial eye over the copy that’s submitted. Meanwhile, keep up the good work!

Your math leaves out a little of the details and your description is slightly inaccurate. As you typed it, the real value of 1872 squared is actually 3,504,384. The 1872 is actually the sum of two squares and the SQUARE ROOT of 1872 is where you get your 43.2, but closer actually to 43.3 if you round it off (43.266666…). So, you don’t divide the diagonal amount, you take the square root of the diagonal value (1872 in your first instance).

With so many people using their smart phones as principal cameras, I wonder how or whether this article would be helpful by talking about sensor sizes in different smart phones? The article stands well on it’s own, but I’m just curious about the phone part (and I don’t even own one).

Stan Hooper,
The form of calculation that the author has used is called RSS, root of the sum of the squares. Its well known in technical (electronic) measurements. The author has not clarified it well.

The author’s observation about smart phones is only to illustrate the comparative limitations of smart phones v/s dedicated photographic devices.

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